Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $24.66   7.273%   $26.4535   $26.45   $26.45   $26.50  
  Purchase #2 $34.43   5.826%   $36.4359   $36.44   $36.45   $36.40  
  Purchase #3 $45.52   5.874%   $48.1938   $48.19   $48.20   $48.20  
  Purchase #4 $38.26   12.489%   $43.0383   $43.04   $43.05   $43.00  
  Purchase #5 $195.85   7.599%   $210.7326   $210.73   $210.75   $210.70  
  Purchase #6 $83.81   9.678%   $91.9211   $91.92   $91.90   $91.90  
  Purchase #7 $217.51   5.520%   $229.5166   $229.52   $229.50   $229.50  
  7 purchase totals = $640.04       $686.2918   $686.29   $686.30   $686.20